This invention relates to fire-proof glass sheets or panes which resist high temperature, and which have such a high thermal strength and dimensional stability that when they are used as a room closure, they withstand a fire test according to DIN 4102 for at least 90 minutes without cracking or causing an opening in the room closure.
It is generally known that in the event of a fire in a building, the glazing in windows, doors and partitions are cracked by the heat which is set up and the broken pieces fall out of the frames. The cracking and falling out of the glazing in the event of a fire is very dangerous for two reasons: firstly, the pieces which fall out can lead to serious injury, and secondly the fire is able to spread from room to room inside the building through the openings which are thereby formed and also from floor to floor over the external wall. Several fires in high buildings have shown what disasters can be the result thereof.
The only glases which are resistant to fire in accordance with DIN 4102 and which have been used for the glazing of buildings are wired or armoured glass and the glass bricks.
However, wired glass and glass bricks are unsuitable for many fields of application. Thus, wired glass cannot be used for optical reasons, for example, as window glazing for residential use. The wire mesh in the wired glass has hitherto always proved to be very disadvantageous, when it was a question of using the glazed opening as a way of escape or as a room closure. Glass bricks can only be used for special purposes because of their high weight and their greatly reduced transparency.
As compared with the normal commerical glass used in buildings, plate glass or float glass, which are very similar as regards their heat expansion, the thermally hardened building glass not only has an increased mechanical strength, but also an increased thermal resistance. Accordingly, these thermally hardened glasses are also used in the parapet zone, in which there can be temperature differences of 100.degree. to 120.degree. C.
Using a fire test according to DIN 4102 (1970 Edition), sheet 2, section 5.2.4 (FIG. 1, curve 1) the single glasses and the thermally hardened glasses consisting of building glass, plate glass or float glass, already crack after 2 to 3 minutes, and consequently the standard as regards fire and the spreading thereof is no longer satisfied. It is true that the wired glass and the glass bricks also crack after 2 to 3 minutes, but as regards these glasses, the cohesion is assured by the wire meshing or by the width of the glass bricks, and fire and smoke are prevented from passing through for at least 60 minutes.
However, if a fire lasts longer than 60 minutes, then the temperature in the glazing enclosing the fire area rises to above the softening temperature of these glasses, so that the glazing is deformed and a passage is made available for the fire and smoke.
It was found that, in a fire test according to DIN 4102, the temperature of a single glazing having a thickness of 7 mm already rises to about 700.degree. C. in a period of 60 minutes on the side further from the fire. With fires lasting a longer time, the temperature of the glass pane rises to above 700.degree. C., so that the softening temperature (10.sup.7.6 poises) of the glass is finally reached and exceeded. At latest on reaching the softening temperature of the glass, however, the glass pane is so strongly deformed that it no longer prevents fire and smoke passing through.
In many cases, however, it is necessary for the glazing in external wall openings, partitions and doors, to withstand a fire for longer than 60 minutes.
Tests have shown that, after 90, 120 and 180 minutes, respectively, in a fire test according to DIN 4102, temperatures of about 800.degree., 850.degree. and 900.degree. C., respectively, occur on the single glazing which is further from the fire and which is enclosing the seat of the fire.